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L24 SAE Horsepower

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Doesn't this depend on how much power is lost in the transmission/u-joints/differential and possibly drain from components like the alternator, etc.? Those numbers would certainly vary depending on which components your car has installed.

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Doesn't this depend on how much power is lost in the transmission/u-joints/differential and possibly drain from components like the alternator, etc.? Those numbers would certainly vary depending on which components your car has installed.

That would be the rwhp rating. I just want the standard SAE motor rated HP and not the HP rating due to drive terrain loss. Though that would also be very interesting to see what a stock 240z would be able to push out.

Though usually, AWD systems lose 30~50hp, RWD lose 15~30hp and FWD lose 10~20hp from the manufactures numbers. So like an Evo, Mitsu says that it has 289hp, but by the time that number gets to the wheels it is more like 250hp due to drive terrain loss.

Though this isnt true all the time because sometimes the ratings are lower than what they really are due to insurance and what not. Like the SRT4 is rated at 230hp, but the rwhp rating is 235hp to 250hp and for the Cobalt SS, that is rated at 205hp, but stock they dyno 230rwhp.

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The 2 dyno operators I've used estimated 15% to 20% for drivetrain loss. Keep in mind that is only when you're in the gear that has a 1:1 ratio (4th gear on both the 4 speed and 5 speed transmissions for Zs). Any other gear has additional losses.

Also, FWIW, at those session we had a few stock 280z cars. They were all around 122 rwhp corrected IIRC. We didn't have any stock 240s but I'd expect it to be less, even accounting for the additional smog equipment of the later 280zs.

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Well, in the 70's the rating was 151/149 for the L24 found in the 240z car. Now with the SAE standards always changing, what would this number be using todays standards?

I would guess it would still be pretty close to the same. The reason is that the 240-Z still doesn't suffer from the accessory loss associated with the average new car. A/C, A/T, Larger Alternators, PS...

Equipped with a modern engine management system and Fuel Injection to meet today's Emissions standards, the L24 would pick up some power, but then it would be lost to stricter emissions.. so it would be an even trade (I'd guess). Not too hard to get 150HP out of a 2.4L OHC engine design today..

Summary from my research on this subject:

SAE Gross HP - any thing goes. Any grade of fuel, no accessory loss, no water nor oil pumps attached, One Run Wonders OK. Most of the engines used to hit their Peak HP ratings were junk after one run. They were also special built, set up loose etc. Very few of them would have ran over 1000 miles in actual use... But They Did Hit, at least once, the Numbers As Advertised.

SAE HP - required a standard production engine be taken at random off the engine line, equipped with oil pump, water pump, fan, distributor, and generator/alternator. It also had to have standard exhaust manifold and header pipe in place.

SAE Net HP - all the above, PLUS all standard accessories found on the average model the engine was installed in. It had to have a full exhaust system, standard air cleaner in place, coolant in circulation and be measured at standard operating temperatures as found in the average model it was installed in.

In 1970/73 the L24 was rated and reported as "SAE HP".... NOT SAE NET and certainly NOT SAE GROSS.

Today - most stock 240-Z's that have been put on chassis dyno's - in good operational condition will produce numbers between 108 and 120 HP at the rear wheels. Most stock 75-78 280Z's will produce 120 to 130 HP at the rear wheels.

Converting Rear Wheel HP to Crankshaft HP ratings... the rule of thumb varies between a loss factor of 20 to 30%. L24's, 150HP x 0.8 = 120HP and/or 150x0.7=105HP. L28's 165HP x 0.8= 132 and/or 165HP x 0.7=115. (California Models with the L28's had lower reported HP numbers.. tuned for stricter emissions and some came with Cat's)

So why didn't the HP Ratings on the L28 drop as greatly between reported SAE HP and SAE Net HP as most American Cars did - The Muscle Cars from 69/72 - dropped greatly in reported HP by 73/75 (some by as much as 30%!!), the L28's did not however drop from a reported 165HP to 108!.

The reason is - the L24 and L28 between 70 and 78 on average all had the same lack of standard accessories. The average American car had to take the additional loss from PS, PB, A/C, larger Alternators etc; all of which were pretty much put on the average model sold. So we saw far greater HP number loss in the typical American Cars when they started using SAE Net... By 1980/82 more and more of the 280ZX's sold were equipped on-average with PS, A/C and larger Alternators... so they too lost a few more HP on the reported numbers.

We also see large variations in reported HP numbers on the L28's - between California Models and the standard US spec. models - because California models had stricter emissions standards (engines de-tuned for emissions plus some models got Cat's earlier etc).

Redesigned combustion chambers etc also account for some small HP loss in the 280ZX's as meeting emissions standards not performance was the main goal.

- - - end summary - - the whole article, still in somewhat of a "draft form" is on the Z Car Home Page: <a href=http://zhome.com/Carl/SAEHPRatings.htm TARGET=NEW> Gross, SAE and SAE Net </a>


Carl B.

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Does anybody actually have a stock Z?
There are a few. My red 240Z is darn close. The only drivetrain modification on it is the exhaust downstream of the factory downpipe. Yes, still running points ignition, and the smog pump and plumbing are intact and operating. Since the replacement exhaust is still only 1 3/4" pipe, the difference from stock is negligible.

But I doubt I'd every bother to dyno it. Don't really care what the numbers are. I just like to drive it.

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V8's could have taken the larger hit on emissions because there is a emissions set, and for a V8 to meet that emissions requirement would be much harder for a small I6 to meet the requirement.

Also, things like A/C, alternator don't really add all that much stress to the motor. Only if you are bagging your sound system, or using your A/C is when you would see a noticeable decrease in performance.

Plus I thought that it was only the L26's that had 165HP. From what I have seen, the L28's initially started out at 135HP due to emissions, but did work its way back up to 145HP and than 180HP in the turbo version.

L24 sure is the sweetest. Smaller motor pushing about the same numbers and ways much much lighter (240z). :smoke:

Actually, I think that the L24 is an extremely efficient motor for its time. Today, if you look around a bit, current 2.4L I4 DOHC push no more than 170hp and can be seen as low as 140hp, and get roughly the same fuel economy. When you think about it, it seems like nothing has progressed when you see 36 years worth of technology put into todays 2.4L's, and the numbers look like the same from a 1970 L24. IMO, even with emission standards, that is a shame. With the dozens of sensors found in cars claiming that they are there to improve fuel economy, and power, in my books that just seems like a load of bs and raises the cost of the car like crazy, mostly due to emissions.

Yeah I know that a manufacture can get 100hp per liter and make a 240hp 2.4L, but there isn't one and 100hp per liter is hard to come by in a N/A set up and rev like a mad man.

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Being a SAE member, here's the summary from SAE themselves:

Horsepower in the US

Brake Horsepower

"Brake Horsepower" was a term commonly used before the 1970s and is sometimes also referred to as "Gross Horsepower." It used an old SAE standard (J245) to perform the measuring. That standard just focused on the measurement side, not the process itself. The term indicates the brake, the device for measuring the true power of the engine. Stating power in 'bhp' gives some indication this is a true reading, rather than a calculated or predicted one. However, several OEMs started to strip their engines of essential ancilliaries for the purposes of getting a high horsepower figure to use in marketing the car.

SAE Horsepower

As part of the passage of the Clean Air Act in 1972 (and also in preparation for it) SAE developed a new engine horsepower testing standard as part of its efforts to meet the new EPA testing regime. That standard was SAE J1349 "Engine Power Test Code – Spark Ignition and Compression Ignition – Net Power Rating Standard" and was pretty much in current use as SAE J1995 as revised - until 2004. J1349 specifies a basis for net engine power rating, and a method for determining net full load engine power with a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.

SAE Horsepower 2004

SAE passed a large scale revision of their horsepower measurement standard (J1349) that's available here:


This is a revision that closes procedure loopholes that manufacturers exploited to get a few more horsepower out of the 1995 version of J1349.

It added the following:

1. Reference inlet air and fuel supply test conditions

2. A revised method for correcting observed power to reference conditions

3. A revised method for determining net full load engine power with an engine dynamometer.

Wheel Horsepower

Since the release of low cost in floor dynamometers a new way of measuring horsepower has gained favor, "Wheel Horsepower." Its based on measuring a vehicle driveline's ability to accelerate a mass with a horsepower number calculated from the mass acceleration measurement. At this point SAE has not released any horsepower rating standards regarding the process, measurement, or calibration of floor dynamometers so the numbers published are not verifiable.

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  • 2 weeks later...

The Capital Z-Car of Texas did a dyno day in 2005 and since it was real inexpensive, I took mine down. It clocked in at 105 HP. The motor is close to stock, but very high miles on the block.

Stock exhaust, E31 head (stock valves) on a '72, Malory ignition, stock alternator, no smog pump, bigger oil pump.


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